Twenty peritoneal specimens, collected from 19 patients at the insertion or removal of the catheter for continuous ambulatory peritoneal dialysis (CAPD), were examined by light microscopy (LM) and transmission and scanning electron microscopy (TEM and SEM). During long-term CAPD, the peritoneal tissue showed an absence of mesothelial cells and a fibrous thickening by proliferation of degenerative collagen fibers. Ultrastructural examination by SEM revealed that the surface of the peritoneum with mesothelial denudation was covered by a continuous sheet of homogeneous material (a membrane structure) in patients in an the early stage of peritonitis. In cases in the advanced stage, the membrane structure covered the irregular collagen bundles, which occasionally showed through breaks in the membrane-like structure. Vascular alterations characterized by the hyalinous degeneration of media, the thickening of the basement membrane in small vasculature, and lymphatic dilatation were observed by TEM in cases of sclerosing peritonitis. Our results suggest that the pathological changes of the peritoneal surface and peripheral blood and lymphatic circulatory impairment may be related to ultrafiltration failure and the progression of pathological process during CAPD
